Experiments were performed on luminally perfused, isolated, canine, jejunal segments in vivo to determine the effects of vasopressin on intestinal motility, myoelectrical activity and absorption. Intravenous vasopressin abolished spike activity and sometimes disrupted slow wave activity. The jejunum became atonic with intraluminal pooling of perfusate. Transit time was prolonged and intestinal absorption of water was decreased. Radionuclide imaging of the intestinal contents showed a doubling of intraluminal volume with vasopressin and confirmed the loss of intestinal motility. It is suggested that the high plasma levels of vasopressin which are known to follow laparotomy may be a factor in the development of postoperative ileus.